Polyethylene terephthalate (PET) is widely used in both flexible and rigid packaging. There is a need to provide polymer films with improved barrier properties to oxygen, carbon dioxide and moisture to accommodate increasing demands in lighter weighting of bottles, simpler designs, and longer shelf life of packaged food, including produce, meat, fish, and cheese and other dairy products. In addition, with the emphasis on technologies based on sustainable chemistry, there has been increased interest in films based on monomers from renewable sources, such as polyethylene furanoate based on furan dicarboxylic acid, which can be produced using bioderived compounds, such as fructose.
Several new polymers with high barrier properties have been developed from either renewable or non-renewable resources and some of these have already been commercialized. These include polyethylene naphthalate (PEN), polyglycolic acid (PGA), and polyethylene furanoate (PEF). For those polymers, the oxygen barrier property (at about 23° C. and 50% relative humidity) follows the order:PGA≈EVOH>PEN≈PEF>PETCompared to PET, PEF has been reported to have six times improved oxygen barrier, two times improved barrier to carbon dioxide, and also improved moisture barrier. “Bioplastics, Reshaping the Industry”, Las Vegas, Feb. 3, 2011.
In WO 2010/077133 (Sipos, assigned to Furanix Technologies B.V.), a process for the production of PEF polymers and copolymers made from 2,5-furandicarboxylate is disclosed. The (co)polymers have a number average molecular weight of at least 10,000 (as determined by GPC based on polystyrene standards), and an absorbance below 0.05 (as a 5 mg/ml solution in a dichloromethane:hexafluoroisopropanol 8:2 mixture at 400 nm). These (co)polymers may be subjected to solid state polycondensation and then attain a number average molecular weight greater than 20,000 (as determined by GPC based on polystyrene standards), without 5 suffering from discoloration.
There remains a need for multilayer films based on cost-effective polymers that form films, preferably clear films, that exhibit a desirable balance of properties, such as improved oxygen permeability, or improved water-vapor transmission rate (WVTR), or, preferably, both.
The present invention achieves these objectives by forming a multilayer film comprising (a) a biaxially-oriented polyethylene furanoate polymer layer, (b) an optional ink layer, (c) a bonding layer, and (d) a sealant layer, wherein the BO-PEF polymer has an O2 gas permeability of less than 0.25 cc-mil/100 in.2 24 hrs atm at 80% relative humidity, or a moisture permeability of less than 0.5 g-mil/100 in.2 24 hrs atm at 38° C., or both.